11

FMECA & Reliability FMECA & Reliability Analysis of an Elastomeric Analysis of an Elastomeric Rotating Scissor Bearing of Rotating Scissor Bearing of

HelicopterHelicopter

Jacques VirasakJacques Virasak

RPI DSES-6070 HV5 RPI DSES-6070 HV5 Statistical Methods for Reliability Engineering Statistical Methods for Reliability Engineering

Spring 2008Spring 2008

3/31/20083/31/2008

22

ObjectivesObjectivesTo perform both FMECA and reliability analyses on a typical helicopter To perform both FMECA and reliability analyses on a typical helicopter main rotor scissor bearing assembly. main rotor scissor bearing assembly.

To evaluate the response of the scissor bearing to failures occurring in To evaluate the response of the scissor bearing to failures occurring in any of its components with respect to aircraft and personnel safety as any of its components with respect to aircraft and personnel safety as well as scissor bearing operational efficiency.well as scissor bearing operational efficiency.

To perform Failure Mode, Effects and Criticality Analysis (FMECA) in To perform Failure Mode, Effects and Criticality Analysis (FMECA) in accordance with MIL-STD-1629A to address the qualitative safety accordance with MIL-STD-1629A to address the qualitative safety requirements identified in the requirement specification. requirements identified in the requirement specification.

To analyze the reliability of the elastomeric shim package of the scissor To analyze the reliability of the elastomeric shim package of the scissor bearing based on both Sikorsky and US government experiences with bearing based on both Sikorsky and US government experiences with laminated elastomeric and metallic shim packaged production parts.laminated elastomeric and metallic shim packaged production parts.

To demonstrate the application of diverse techniques learned To demonstrate the application of diverse techniques learned throughout the current reliability analysis classes.throughout the current reliability analysis classes.

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If An Rotating Scissor Bearing If An Rotating Scissor Bearing (RSB) Fails…(RSB) Fails…

The loss of relative motion between the rotating scissors The loss of relative motion between the rotating scissors and the rotating swashplate will result in loss of the and the rotating swashplate will result in loss of the controllability of the main rotor, increase rotor vibration, controllability of the main rotor, increase rotor vibration, and decrease response to control input. and decrease response to control input.

The loss of load transmission from the rotating scissor to The loss of load transmission from the rotating scissor to the rotating swashplate will create an unbalanced rotor the rotating swashplate will create an unbalanced rotor and increase rotor vibration.and increase rotor vibration.

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What Is An Elastomeric RSB?What Is An Elastomeric RSB?

Outer Member

Inner Member

Metallic Shims

andElastomeric

Shims

ZZ

Bushings

Sleeve

K1 K2 K10 K11K5 K6

Force Force

55

Failure Mode, Effects and Criticality Analysis Failure Mode, Effects and Criticality Analysis (FMECA)(FMECA)

OuterMember

InnerMember

MetallicShims

ElastomericShims

66

RAPTOR vs. TheoryRAPTOR vs. Theory

The discrepancy is RAPTOR run driven

Run T=3,000 hr. T = 2,400 hr.1000 0.272 0.350500 0.282 0.348250 0.280 0.340125 0.288 0.352Avg. 0.281 0.348

Theory 0.287 0.368Delta 2.12% 7.13%

Run T=3,000 hr. T = 2,400 hr.1000 0.272 0.350500 0.282 0.348250 0.280 0.340125 0.288 0.352Avg. 0.281 0.348

Theory 0.287 0.368Delta 2.12% 7.13%

77

Monte Carlo vs. TheoryMonte Carlo vs. TheoryMTBF vs. Replacement Time

1200.00

1250.00

1300.00

1350.00

1400.00

1450.00

1500.00

1550.00

1600.00

1650.00

1800 1900 2000 2100 2200 2300 2400 2500 2600 2700

Replacement Time, to [hr]

MT

BF

[h

r]

Monte Carlo C = CA/Cinf

TheoryC = CA/Cinf

The discrepancy is < 3%

Cost vs. Replacement Time

1.08

1.09

1.10

1.11

1.12

1.13

1.14

1.15

1800 1900 2000 2100 2200 2300 2400 2500 2600 2700

Replacement Time, to [hr]

Co

st, C

= C

A /

Cin

f

Monte Carlo C = CA/Cinf

TheoryC = CA/Cinf

88

Monte Carlo – Weibull vs. TheoryMonte Carlo – Weibull vs. Theory

C

PD

F

12000800040000

0.00045

0.00030

0.00015

0.00000

C

Perc

ent

1000

00.0

1000

0.0

1000

.0

100.

010

.01.0

0.1

99.999050

10

1

0.01

C

Perc

ent

12000800040000

100

50

0

C

Rate

12000800040000

0.00044

0.00042

0.00040

0.00038

Table of Statistics

Median 1704.78IQR 2812.65Failure 1000

Censor 0AD* 0.334

Shape

Correlation 0.999

0.964502Scale 2492.88

Mean 2533.07StDev 2626.81

Probability Density Function

Survival Function Hazard Function

Distribution Overview Plot for CLSXY Estimates-Complete Data

Weibull

99

ConclusionsConclusions

Elastomeric RSB is an on-condition Elastomeric RSB is an on-condition replacement and non-repairable part.replacement and non-repairable part.

FMECA was used to ensure the save usage of FMECA was used to ensure the save usage of the elastomeric RSB.the elastomeric RSB.

Diverse reliability analytical tool and Diverse reliability analytical tool and techniques were successfully used to analyze techniques were successfully used to analyze the elastomeric RSB. the elastomeric RSB.